When turnabout is indeed fair play

Mexico Set, by Len Deighton. New York: Alfred A. Knopf. 374 pp. $16.95. Defections in espionage fiction are not unusual. Len Deighton's new novel, ``Mexico Set,'' however, deals with two: Fiona Samson's exposure as a double agent and escape to East Berlin in last year's ``Berlin Game''; and the current assignment of her husband, British intelligence agent Bernard Samson, which is to persuade Soviet agent Erick Stinnes to defect to London.

``Mexico Set'' doesn't really get going until Page 139. That's when the young woman who has gotten into Samson's car on the pretext that hers won't start pulls out a hypodermic needle and orders Samson to drive to London's Heathrow Airport.

At Heathrow, Samson meets his wife, now the top KGB officer in East Berlin and Stinnes's boss. Fiona offers to make a deal: She will leave their two young children, who live with Samson's mother, alone for at least a year if Samson will forget about recruiting Stinnes. At this point, ``Mexico Set'' becomes a whole new ball game, or should I say tennis match?

``Berlin Game'' and ``Mexico Set'' are the first two-thirds of what the publisher, Knopf, calls Deighton's game/set/match trilogy. ``Mexico Set'' picks up where ``Berlin Game'' left off.

Samson's position in MI6 has been compromised, and until his superiors can lay to rest their suspicions concerning his knowledge of and involvement in Fiona's activities, he won't be fully trusted. They know that Stinnes can provide the information that will clear or condemn Samson conclusively. Fiona's proposal creates a dilemma for Samson: Will he be able to keep both his job and his children?

As he did in ``Berlin Game,'' Deighton provides an in-depth look at the interdepartmental politics, the clash of personalities, and the jockeying for position within British intelligence. It is the wheeling and dealing, the convoluted motives, and the uncertainty about why things are happening that give suspense to this novel.

The action moves from Mexico to London, Berlin, Paris, and back to Mexico, with Deighton providing the atmosphere, especially in the Mexican sections, which he does so well. The characters, most of whom appeared in ``Berlin Game,'' are interesting, especially Samson, who is, in the tradition of the best spies, outwardly somewhat colorless and inwardly intriguing.

There is a sudden, shoot-'em-up ending, which manages to conclude Samson's immediate concerns while leaving a lot of uncertainties and loose ends. Presumably these will be tied up in the third novel. Samson wins the set, but who will win the match?

A regular monthly column in the Book Review.